User's Manual

3. Functional Descriptions
3.1. MCU
ESP8266EX is embedded with Tensilica L106 32-bit micro controller (MCU), which features extra low power
consumption and 16-bit RSIC. The CPU clock speed is 80MHz. It can also reach a maximum value of
160MHz.
ESP8266EX is often integrated with external sensors and other specific devices through its GPIOs; codes
for such applications are provided in examples in the SDK.
3.2. Memory Organization
1. Internal SRAM and ROM
ESP8266EX WiFi SoC is embedded with memory controller, including SRAM and ROM. MCU can visit the
memory units through iBus, dBus, and AHB interfaces. All memory units can be visited upon request, while a
memory arbiter will decide the running sequence according to the time when these requests are received by the
processor.
According to our current version of SDK provided, SRAM space that is available to users is assigned as
below:
 RAM size < 36kB, that is to say, when ESP8266EX is working under the station mode and is connected
to the router, programmable space accessible to user in heap and data section is around 36kB.)
 There is no programmable ROM in the SoC, therefore, user program must be stored in an external SPI
flash.
2. External SPI Flash
This module is mounted with an 2 MB external SPI fl ash to store user programs. If larger definable storage
space is required, a SPI fl ash with larger memory size is preferred. Theoretically speaking, up to 16 MB
memory capacity can be supported.
Suggested SPI Flash memory capacity:
 OTA is disabled: the minimum fl ash memory that can be supported is 512 kB;
 OTA is enabled: the minimum fl ash memory that can be supported is 1 MB.